Composition-dependent propagation of manufacturing uncertainty in the open-circuit sensitivity of ScAlN piezoelectric MEMS hydrophones

Scandium-doped aluminum nitride (ScAlN) is widely used in high-performance piezoelectric MEMS hydrophones, where material composition strongly affects device performance. However, the influence of Sc-composition fluctuations on uncertainty propagation and manufacturing robustness remains unclear. This study develops a composition-dependent uncertainty analysis framework based on an experimentally validated benchmark multiphysics finite element model. By extrapolating from simulation results, geometric parameters and Sc content are treated as random variables to evaluate manufacturing uncertainty at different doping concentrations. The results show that increasing the Sc concentration improves the nominal open-circuit sensitivity but also increases the device response to composition fluctuations. This creates a trade-off between sensitivity enhancement and manufacturing robustness. As the Sc concentration increases, the dominant uncertainty source shifts from geometric tolerances to material-composition variations, indicating that Sc doping changes the propagation pathway of manufacturing errors. Increasing the nominal Sc concentration alone does not significantly broaden the output distribution. Output uncertainty increases only when higher Sc concentrations are accompanied by larger composition variations. These findings clarify the composition-dependent uncertainty propagation mechanism and provide guidance for adaptive tolerance allocation, manufacturing optimization, and reliability-oriented design of ScAlN piezoelectric MEMS devices.